In certain disease states, the heart lacks sufficient pumping capacity to meet the needs of the body. This inadequacy can be alleviated by providing a mechanical pumping device referred to as a blood pump, one example of which is a ventricular assist device (“VAD”). A VAD, for example, acts in parallel with a patient's left ventricle to impel blood from the ventricle into the aorta, and thus supplements the pumping action of the heart.
A blood pump is typically connected, e.g., installed, outside of the heart. In the instance of a VAD, it may include an inlet cannula connecting the interior of the left ventricle to the intake of the pump. The VAD may also include an outlet tube connected between the outlet of the pump and the aorta. Once connected to a ventricle, the VAD and the heart act in parallel to pump blood from the left ventricle to the aorta. A blood pump in a typical human patient should be capable of providing substantial blood flow, as, for example, a few liters per minute or more, against a pressure head corresponding to the blood pressure of the patient. For example, one typical operating condition for a blood pump involves pumping 5 liters of blood flow at a pressure head of 75 mmHg. Pressure head is known as the difference in pressure between the outlet and the inlet of the pump, where a positive number indicates higher pressure at the outlet.
Implantable blood pumps should also be compact so as to facilitate mounting the pump within the patient's body. An implantable blood pump should further be efficient so as to minimize the power required to operate the pump, for example, by reducing the rotational speed needed to achieve a particular pressure head. Moreover, the pump should be designed to minimize damage to the patient's blood. It should limit the amount of blood subjected to relatively high shear stresses, for example, 150 Pa or more, so as to minimize the damage to components of the blood. Ideally, and in addition to these attributes, a blood pump should remain in operation for months or years to keep a patient alive, or indefinitely at least until the heart heals or a suitable donor heart becomes available if the heart does not heal.
One form of a blood pump is disclosed in U.S. Pat. No. 8,852,072. The pump includes a pump housing having an impeller and a diffuser disposed within the pump housing. The impeller has a linear body extending along an axis and blades projecting outwardly from the body and curving around the axis in a substantially helical pattern having a pitch angle which varies along the axial length of the impeller. A power source provides the means to actuate the impeller, causing it to impel blood axially in the housing in a downstream direction towards a linear diffuser. The diffuser includes vanes projecting radially outward from the body. The pump generates pressure head for blood entering through an inlet of the housing and exiting into the aortic valve. Although prior art pumps can generate pressure to pump blood, further improvements as described above would be desirable.
Accordingly, there is a need for an implantable blood pump which is sized so that a diffuser region of a housing having a diffuser disposed therein does not extend into an aortic valve when implanted in a ventricle. There is also a need for a pump which produces greater pressure head through the pump relative to prior art designs while simultaneously reducing shear stresses within the housing.